(Reuters) - Some civilians were evacuated from a Palestinian refugee camp on the Damascus outskirts, the United Nations said on Sunday, fleeing an advance by Islamic State and more that two years of government siege that has led to starvation and disease.

The Islamic State group has taken most of Yarmouk camp from rival insurgents while the army surrounds the district, only a few kilometres from President Bashar al-Assad's palace.

U.N. Relief and Works Agency (UNRWA) spokesman Chris Gunness said 94 civilians, including 43 women and 20 children, made it out of the camp on Sunday and were provided with humanitarian support.

There are still 18,000 people in the camp, a mixture of Palestinians and Syrians, according to the UNRWA. Yarmouk became a battleground before the siege, and has been devastated by street fighting, air attacks and shelling.

The Syrian Observatory for Human Rights, which monitors the conflict from Britain, said hundreds had fled over the past two days.

"There have been some civilians who were able to flee the camp earlier today and we call on all parties to show maximum restraint so other civilians who wish to leave can be evacuated," Gunness said in an email.

The Observatory said the Syrian air force dropped crudely-made barrel bombs on Yarmouk on Sunday. Syrian state media did not report that civilians had been evacuated.

Saeb Erekat, from the executive committee of the Palestine Liberation Organization (PLO), called on Saturday for the an evacuation of civilians. "Reports of kidnappings, beheadings and mass killings are coming out from Yarmouk," he said.

"For over 700 days, the camp has been the victim of a draconian siege, which has resulted in the death by starvation of at least 200 Palestinians. The PLO, through its envoys, has been trying for years to lift the siege."

Islamic State rules swathes of eastern Syria and Iraq and is the target of a U.S.-led campaign of airstrikes.

The group posted photos on Sunday of its fighters inside the camp. It also showed a photo of 13 men kneeling and facing a wall. The caption described them as rival fighters from Aknaf Beit al-Maqdis, an anti-Assad militia of Syrians and Palestinians from the camp.

Yarmouk was home to half a million Palestinians before the Syrian conflict began in 2011. The war has killed 220,000 people and displaced millions.

(Reporting by Oliver Holmes in Beirut and Mostafa Hashem in Cairo, editing by Clelia Oziel)